The dynamics of multiple populations in the globular cluster NGC 6362

Abstract

We investigate how the Milky Way tidal field can affect the spatial mixing of multiple stellar populations in the globular cluster NGC 6362. We use N-body simulations of multiplepopulation clusters on the orbit of this cluster around the MilkyWay. Models of the formation of multiple populations in globular clusters predict that the second population should initially be more centrally concentrated than the first. However, NGC 6362 is comprised of two chemically distinct stellar populations having the same radial distribution. We show that the high mass-loss rate experienced on this cluster's orbit significantly accelerates the spatial mixing of the two populations expected from two-body relaxation. We also find that for a range of initial second-population concentrations, cluster masses, tidal filling factors and fraction of first-population stars, a cluster with two populations should be mixed when it has lost 70- 80 per cent of its initial mass. These results fully account for the complete spatial mixing of NGC 6362, since, based on its shallow present-day mass function, independent studies estimate that the cluster has lost 85 per cent of its initial mass.